Heat exchanger for a motor vehicle

ABSTRACT

An exhaust gas heat exchanger for a motor vehicle may include an outer tube extending along a longitudinal direction to be flowed-through by a hot gas. The outer tube may define an outer tube interior space and in a cross section perpendicular to the longitudinal direction may include at least two outer tube-tube walls. An inner tube may be arranged in the outer tube interior space and may extend along the longitudinal direction. A longitudinal end of the inner tube may be closed and may define an inner tube interior space and in the cross section perpendicular to the longitudinal direction, may include at least two inner tube-tube walls at least one of which may include a plurality of apertures. A plurality of thermoelectric modules may be arranged on an outside of the at least two outer tube-tube walls and may each include a hot side and a cold side.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Application DE 10 2017 210 276.4 filed on Jun. 6. 2017 and German Application DE 20 2016 008 278.8 filed on Nov. 29, 2016, the contents of each of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a heat exchanger, in particular an exhaust gas heat exchanger, for a motor vehicle. The invention, furthermore, relates to a motor vehicle with an internal combustion engine, comprising an exhaust system and such a heat exchanger interacting with the exhaust system.

BACKGROUND

Heat exchangers are employed in combination with exhaust systems of internal combustion engines in order to render utilisable the heat contained in the exhaust gas. For this purpose, thermoelectric modules with thermoelectric elements can be provided in the heat exchanger. Such thermoelectric elements consist of thermoelectric semiconductor materials, which convert a temperature differential into a potential differential, i.e. into an electric voltage and vice versa. In this way, heat energy from the heat exchanger can be converted into electric energy. Physically, the thermoelectric modules are based on the Seebeck effect when they convert heat into electric energy. Within a thermoelectric module, p-doped and n-doped thermoelectric elements are interconnected. Usually, a plurality of such thermoelectric modules is interconnected to form a thermoelectric generator, which can generate electric energy or an electric voltage from a temperature differential in conjunction with a corresponding heat flow. In the heat exchanger, the temperature differential between the hot sides and the cold sides of the thermoelectric modules required for generating electric energy is generated in that the hot gas with the hot sides and a coolant with a temperature that is lower compared to the hot gas is brought into thermal interaction with the cold sides of the thermoelectric modules. This is achieved in that the hot sides and cold sides of the thermoelectric modules are suitably arranged in the heat exchanger flowed-through by the hot gas and by the coolant.

The present invention therefore deals with the problem of stating an improved or at least another embodiment for a heat exchanger of the type described above, which is characterized by an improved efficiency.

This object is solved through the subject of the independent patent claims. Preferred embodiments are subject of the dependent patent claims.

SUMMARY

Accordingly, the general basic idea of the invention is to arrange thermoelectric modules with thermoelectric elements in a heat exchanger in such a manner that the hot gas conducted through the heat exchanger strikes the hot sides of the thermoelectric modules in the form of an impact jet. This has the consequence that a particularly high quantity of heat is extracted from the hot gas, which, following the operating principle of a thermoelectric generator, can be converted into electric energy by the thermoelectric modules. This is accompanied by an improved efficiency of the heat exchanger which proves to be particularly advantageous when the same is operated as exhaust gas heat exchanger in order to render utilisable the energy contained in the exhaust gas of an internal combustion engine.

A heat exchanger according to the invention, which can preferentially be employed as exhaust gas heat exchanger, comprises an outer tube extending along a longitudinal direction for being flowed-through by hot gas, which delimits an outer tube interior space and for this purpose comprises two outer tube-tube walls in a cross section perpendicular to the longitudinal direction. In the outer tube interior space, preferentially coaxially to the outer tube, an inner tube for being flowed-through by the hot gas extending along the longitudinal direction is arranged, which delimits an inner tube interior space. At a longitudinal end, the inner tube is designed closed and, in the cross section perpendicularly to the longitudinal direction, comprises at least two inner tube-tube walls. Furthermore, a plurality of apertures is formed in the inner wall tube walls. By means of said apertures, the inner tube interior space fluidically communicates with the outer tube interior space. The heat exchanger according to the invention additionally comprises a plurality of thermoelectric modules arranged on an outside of the outer tube-tube walls. The thermoelectric modules each have a hot side facing the outer tube and a cold side facing away from the outer tube. In addition, the heat exchanger comprises at least one coolant tube for being flowed-through by a coolant, which is arranged on the cold side of at least one thermoelectric module.

Substantial for the invention in the case of the thermoelectric heat exchanger introduced here is a surface area-enlarging structure provided on the outer tube inside, i.e. on the hot side of the thermoelectric modules. The term surface area-enlarging structure is to mean any mechanical structures whatsoever such as for example protrusions etc. which enlarge the surface area of the inside of the outer tube or of the outer tube-tube wall of the outer tube. By means of such a surface area-enlarging structure, the effective interactive area, which is available to the impact jet striking the outer tube for transmitting heat to the thermoelectric modules, is increased. This results in an improved heat transfer of heat energy from the impact jet to the thermoelectric modules. As a consequence, correspondingly more electric energy is generated by the thermoelectric modules acting as thermoelectric generators which in turn increases the efficiency of the entire heat exchanger. Independently of this, the flow direction of the impact jet can also be influenced with the help of the surface area-enlarging structure before and after the same strikes the outer tube where it is reflected. Thus it is possible, for example, to direct the reflected impact jet so that subsequent impact jets striking the outer tube are not disturbed by the reflected impact jet or only to a minor extent. Thus it is ensured that the impact area, i.e. that area of the outer tube on which the thermoelectric modules are arranged on the outside, can be impinged with as little interference as possible. In other words, it can be ensured with the help of the surface area-enlarging structure, that the geometric and the aerodynamic stagnation point of the impact jet are identical and thus the angle of the deflection of the impact jet during the reflection assumes a zero value.

According to a preferred embodiment, the surface area-enlarging structure is arranged, with respect to the longitudinal direction, in the region of at least one thermoelectric module. In this way it is ensured that the enlarging heat exchange in the region of the thermoelectric modules is possible so that these can absorb an increased amount of heat from the impact jet or the hot gas.

According to a preferred embodiment, the at least one surface area-enlarging structure is located opposite at least one aperture. In this way it is ensured that the hot gas exiting from the aperture at least partly strikes the surface area-enlarging structure. This measure also ensures that the enlarged heat exchange takes place in the region of the thermoelectric modules so that the thermoelectric modules can absorb an increased heat quantity from the impact jet or the hot gas.

Practically, the surface area-enlarging structure projects away from the at least one outer tube-tube wall to the inside, towards the inner tube. Particularly preferably, the surface area-enlarging structure is integrally moulded on the outer tube. This allows creating the surface area-enlarging structure directly during the course of the outer tube production. This results in cost advantages during the production of the heat exchanger.

In an advantageous further development, the surface area-enlarging structure is formed by a plurality of protrusions which project away from the respective outer tube-tube wall towards the inner tube. By means of this measure, a particularly large surface area enlargement can be achieved in a relatively small area section of the outer tube-tube wall. At the same time, such protrusions can be produced technically in a relatively simple manner which simplifies the production of the structure and thus results in cost advantages. Finally, said protrusions are tied mechanically and thus also thermally to the outer tube-tube wall only in well-defined places, as a result of which the heat transfer of hot gas or impact jet to the outer tube-tube wall and thus also to the thermoelectric modules can be homogenised.

Practically, the protrusions are formed as webs which extend, spaced from one another along an extension direction subject to forming intermediate spaces. By means of such webs, a particularly high surface area enlargement can be achieved in little installation space.

Particularly preferably, the protrusions or webs extend linearly, in a top view of the outer tube-tube wall, along the extension direction at least in sections. Alternatively, a non-linear, in particular a curved extension of the protrusions or webs is also possible. A combination by sections of linearly and non-linearly designed protrusions or webs is also conceivable. Conceivable, in particular, is a wave-shaped or polynomial geometry of a projection or web. In each mentioned case, the webs cannot only be used for enlarging the interactive area but additionally also as flow directing elements, which advantageously influence the flow direction of the hot gas or impact jet, in particular before and/or after the reflection on the outer tube-tube wall.

Particularly preferably, the protrusions or webs can have a wave-like geometry in the top view. In this way, an undesirable pressure loss in the impact jet or in the hot gas when flowing through the intermediate spaces between the adjacent protrusions or webs can be kept low.

According to another preferred embodiment, a plurality of webs forms a web group. The webs of such a web group extend radially away from a virtual centre point defined on the outer tube-tube wall. By means of this version, an even reflection of the hot gases or impact jet on the outer tube wall can be ensured.

Preferably, a plurality of web groups is arranged on the outer tube-tube wall preferentially grid-like with at least two grid columns and/or with at least two grid lines.

Practically, the protrusions or webs can be arranged parallel to one another.

In an advantageous further development, the protrusions or web comprise multiple interruptions along the extension direction. The interruptions are realised in such a manner that, by these, two adjacent intermediate spaces are fluidically interconnected in each case.

In an advantageous further development, the interruptions of adjacent protrusions or webs can be arranged staggered relative to one another in the extension direction. The staggered arrangement in this case is preferentially arranged in such a manner that because of the interruptions that are arranged in an staggered manner, communication channels are formed which fluidically interconnect a plurality of adjacent intermediate spaces. By means of such a fluid connection it can be achieved that the impact jet or the hot gas is evenly distributed over the regions of the outer tube-tube wall in which the thermoelectric modules are also arranged. Such a homogenisation of the heat exchange leads to a further efficiency increase of the heat exchanger.

In a particularly advantageous further development, a channel direction, along which the communication channels extend, forms an acute angle with the extension direction of the protrusions or webs.

In an advantageous further development, at least one aperture is present in at least one web, which interconnects to adjacent intermediate spaces. In a further development, a plurality of such apertures can also be arranged spaced from one another in the web. By means of this measure it can also be achieved that the hot gas is evenly distributed over the regions of the outer tube-tube wall, on which the thermoelectric modules are arranged. Such a homogenisation of the heat exchange leads to a further efficiency increase of the heat exchanger.

According to another preferred embodiment, the surface area-enlarging structure comprises a plurality of, preferentially dimpled, protrusions and/or of, preferentially dimpled, recesses. The protrusions or recesses in this embodiment are arranged grid-like on the inside of the outer tube-tube wall. Such a grid-like arrangement of protrusions or recesses in the form of dimples allows providing a plurality of surface area-enlarging elements on relative little installation space. In an advantageous further development, the grid-like arrangement therefore comprises at least two grid columns, preferentially a plurality of grid columns, wherein adjacent grid columns are alternately formed by protrusions and recesses. It goes without saying that a plurality of grid lines can also be provided.

In an advantageous further development, the dimpled protrusions and/or recesses have a round, preferentially circular, geometry in the top view of the outer tube-tube wall.

In another advantageous further development, the protrusions taper, preferentially conically, away from the outer tube-tube wall.

According to another preferred embodiment, the surface area-enlarging structures are designed flat. In a version that is alternative to the former, the surface area-enlarging structure comprises at least one first flat section, which merges into a second flat section, which is arranged at an angle, preferentially at an obtuse angle relative to the first section. By means of this embodiment, the reflection behaviour of the impact jet can be adapted to different user-specific requirements.

According to a further preferred embodiment, the outer tube-tube wall with the surface area-enlarging structure is designed flat. In a version that is alternative to the former, the outer tube-tube wall with the surface area-enlarging structure comprises at least one first flat wall section, which merges into a second flat wall section, which is arranged at an angle, preferentially at an obtuse angle, to the first wall section. The reflection behaviour of the impact jet can also be adapted to different user-specific requirements by means of this embodiment.

The invention additionally relates to a heat exchanger arrangement with at least two heat exchangers which are arranged on top of one another and introduced further up, which can be preferentially stacked onto one another. The heat exchangers of the heat exchanger arrangement fluidically communicate with one another via a common gas outlet. The advantages of the heat exchanger explained further up are therefore transferred also to the heat exchanger arrangement according to the invention.

The invention, furthermore, relates to a motor vehicle with an internal combustion engine having an exhaust system and a heat exchanger according to the invention introduced above. The advantages of the heat exchanger explained above are therefore transferred also to the motor vehicle according to the invention.

Further important features and advantages of the invention are obtained from the subclaims, from the drawings and from the associated figure description by way of the drawings.

It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention.

Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein same reference characters relate to same or similar or functionally same components.

DETAILED DESCRIPTION OF THE DRAWINGS

It shows, in each case schematically:

FIG. 1 an example of a heat exchanger configured as exhaust gas heat exchanger in a longitudinal section,

FIG. 2 the heat exchanger of FIG. 1 in a cross section perpendicularly to the longitudinal direction of the heat exchanger,

FIG. 3 a section through a U-shaped coolant tube of the heat exchanger,

FIG. 4 a version of the heat exchanger according to the FIGS. 1 and 2, in which the coolant tubes, other than with the example of FIG. 1, do not extend in longitudinal direction, but transversely to the same,

FIG. 5-23 various configurations of the surface area-enlarging structure that is substantial for the invention.

DETAILED DESCRIPTION

FIG. 1 shows, schematically, an example of a heat exchanger 1 configured as exhaust gas heat exchanger. According to FIG. 1, the heat exchanger 1 has an outer tube 2 extending along a longitudinal direction L for being flowed-through by a hot gas H, which delimits an outer tube interior space 3. In the outer tube interior space 3, an inner tube 4, likewise for being flowed-through by the hot gas H, is arranged, which delimits an inner tube interior space 5.

The outer tube 2 is designed as flat tube 30 with a first outer tube-tube wall 31 a and a second outer tube-tube wall 31 b located opposite the first outer tube-tube wall 31 a. A part of the thermoelectric modules 10—described as first thermoelectric elements 10 a in the following—are arranged on the first outer tube-tube wall 31 a according to the FIGS. 1 and 2. The remaining thermoelectric elements 10—described as second thermoelectric elements 10 b in the following—are arranged on the second outer tube-tube wall 31 b. The inner tube 4, in the exemplary scenario, is also designed as flat tube 32 with a first inner tube-tube wall 33 a and a second inner tube-tube wall 33 b located opposite the first inner tube-tube wall 33 a.

FIG. 2 shows the heat exchanger 1 of FIG. 1 in cross section perpendicularly to the longitudinal direction L along the section line II-II of FIG. 1. It is evident that the two outer tube-tube walls 31 a, 31 b in cross section perpendicularly to the longitudinal direction L each form a wide side 34 a, 34 b of the outer tube 2 realised as flat tube 30. Furthermore, the flat tube 30 forming the outer tube 2 comprises, in the cross section perpendicularly to the longitudinal direction L, two narrow sides 34 c, 34 d. The aspect ratio of one of the two wide sides 34 a, 34 b to one of the two narrow sides 34 c, 34 d is more than 1, preferentially at least 2, most preferentially at least 4.

In the cross section perpendicularly to the longitudinal direction L, the two inner tube-tube walls 33 a, 33 b each form a wide side 35 a, 35 b of the inner tube 4 realised as flat tube 32. Furthermore, the flat tube 32 forming the inner tube 4 comprises two narrow sides 35 c, 35 d in the cross section perpendicularly to the longitudinal direction L. The side ratio of one of the two wide sides 35 a, 35 b to one of the two narrow sides 35 c, 35 d is more than 1, preferentially at least 2, most preferentially at least 6.

According to FIG. 2, the first outer tube-tube wall 31 a, in the cross section perpendicularly to the longitudinal direction L, faces the first inner tube-tube wall 33 a. The second outer tube-tube wall 31 b accordingly faces the second inner tube-tube wall 33 b.

In the example of the FIGS. 1 and 2, the heat exchanger 1 additionally comprises a first coolant tube 13 a and a second coolant tube 13 b for being flowed-through by a coolant K, which has a lower temperature than the hot gas H. The coolant tubes 13 a, 13 b are thus arranged on the cold sides 12 of the thermoelectric modules 10, so that the coolant K flowing through the coolant tubes 13 can thermally couple to the cold sides 12 of the thermoelectric modules 10.

The first coolant tube 13 a is arranged on the cold sides 12 of the first thermoelectric modules 10 a. The second coolant tube 13 b is arranged on the cold sides 12 of the second thermoelectric modules 10 b. The outer tube 2 in this case is arranged along a stacking direction S, which runs transversely to the longitudinal direction L of the outer tube 2, between the first and the second coolant tube 13 a, 13 b. In this way, the installation space required in stacking direction S for the heat exchanger 1 can be kept small. Each of the coolant tubes 13 a, 13 b can also be designed as flat tube 36, the wide sides 37 a of which face the first or second thermoelectric modules 10 a, 10 b in the cross section perpendicularly to the longitudinal direction L.

The inner tube 4 is designed closed at a first longitudinal end 26 a. To this end, the inner tube has a front wall 16. At a second longitudinal end 26 b of the inner tube 4 located opposite the first longitudinal end 26 a, a gas inlet 27, by contrast, follows the inner tube 4 for introducing the hot gas H into the inner tube 4. In other words, the inner tube 4 is designed open at the second longitudinal end 26 b. In the first inner wall tube wall 33 a and in the second inner wall tube wall 33 b of the inner tube 4, a plurality of apertures 7 is formed in each case, by means of which the inner tube interior space 5 fluidically communicates with the outer tube interior space 3. In this way, the hot gas H flowing through the outer tube 2 can be thermally coupled to the hot sides 11 of the thermoelectric modules 10.

FIG. 3 shows a top view of the coolant tube 13 a in a viewing direction B indicated in FIG. 1 by means of an arrow, which extends perpendicularly to the longitudinal direction L and runs opposite to the stacking direction S. The first coolant tube 13 a in the example of FIG. 3 has a U-shaped geometry with a base 38 and a first and a second leg 39 a, 39 b. The two legs 39 a, 39 b extend along the longitudinal direction L of the outer tube 2. At a first longitudinal end 24 a (see FIG. 1) of the outer tube 2, a coolant distributor 41 is present, which fluidically communicates with a coolant inlet 43 of the first coolant tube 13 that is present on the first leg 39 a. Likewise, a coolant manifold 42 is present at the first longitudinal end 24 of the outer tube 2, which fluidically communicates with a coolant outlet 44 of the first coolant tube 13 a that is present on the second leg 39 b. The two coolant tubes 13 a, 13 b can be designed as identical parts. In this case, the second coolant tube 13 b is likewise designed as shown in FIG. 3.

By way of the FIG. 1, the flow of hot gas H through the heat exchanger 1 is explained in the following. Via the gas inlet 27, the hot gas H is introduced into the inner tube interior space 5 delimited by the inner tube 4 and flows through the same along the longitudinal direction L (see arrows 21 a). Since the inner tube interior space 5 is delimited in longitudinal direction L by the front wall 16 of the inner tube 4, the hot gas H can leave the inner tube interior space 5 only along the stacking direction S, i.e. transversely to the longitudinal direction L through the apertures 7 formed in the first or second inner tube-tube wall 33 a, 33 b (see arrows 21 b). Because of the stagnation pressure forming in the inner tube interior space 5 in the hot gas H, the hot gas H while flowing through the apertures 7 is accelerated and strikes the first respectively second outer tube-tube wall 31 a, 13 b of the outer tube 2 (see arrows 21 c) in the form of an impact jet in each case. Here, thermal energy is passed on to the thermoelectric modules 10. The hot gas H which rebounds from, i.e. is reflected on the outer tube walls 31 a, 31 b can leave the heat exchanger 1 by way of two gas outlets 23 a, 23 b that are present on the outer tube 2 (see FIG. 2), which extend along the stacking direction S (see arrows 21 d). In the scenario of the FIGS. 1 and 2, the outer tube 2 is designed closed at one of the two longitudinal ends 24 a, 24 b located opposite along the longitudinal direction. The outer tube 2 in this case is closed by a front wall 25. This allows an advantageous discharge of the hot gas H in the outer tube 2 in two directions (see arrows 21 c in FIG. 2) that are opposed to one another, which, to the relevant person skilled in the art is known as “medium cross flow”.

FIG. 4 illustrates a version of the example of FIG. 1, in which the outer tube 2 at the longitudinal end 24 a is designed open for discharging the hot gas H. This allows an advantageous discharge of the hot gas H in only one direction (see arrows 21 d in FIG. 4) via a gas outlet 23 c, which, at the first longitudinal end 24 a, follows the outer tube 2. This scenario is known to the relevant person skilled in the art as “maximum cross flow”. In a version that is not shown in more detail in the figures, the alternatives “maximum cross flow” and “medium cross flow” can also be combined.

The heat exchanger 1 according to FIG. 4 comprises three first coolant tubes 13 a and three second coolant tubes 13 b. In versions, the number of first and second coolant tubes 13 a, 13 b can vary. The first and second coolant tubes 13 a, 13 b are each arranged spaced from one another along the longitudinal direction L according to FIG. 4 and extend each along a transverse direction Q running perpendicularly both to the longitudinal direction L and also to the stacking direction S. The representation of the FIGS. 1, 2 and 4 shows that a surface area-enlarging structure 50 each is formed on the insides 62 of the outer tube-tube walls 31 a, 31 b. The surface area-enlarging structures 50 are only schematically indicated in FIG. 1. The surface area-enlarging structures 50 extend, with respect to the longitudinal direction L, across regions of the outer tube walls 31 a, 31 b, in which on the outside the thermoelectric modules 10 are arranged. As is additionally shown by the FIGS. 1, 2 and 4, the surface area-enlarging structures are located opposite the apertures 7, so that the hot gas H exiting the apertures 7 at least partly strikes the surface area-enlarging structures 50 as impact jet.

The FIGS. 5 to 23 show various configuration possibilities of the surface area-enlarging structures 50 in the outer tube-tube wall 31 a. The FIGS. 5 to 23 show, for the sake of clarity, only an extract of the outer tube-tube wall 31 a in each case with a single surface area-enlarging structure 50. The examples of the FIGS. 5 to 23 can be combined with one another insofar as practical. In the FIGS. 5 to 23, the outer tube-tube wall 31 a is exemplarily shown in each case. It goes without saying that the configurations shown in the FIGS. 5 to 18 can also be realised in the outer tube-tube wall 31 b (not shown).

In the perspective representation of FIG. 5, the surface area-enlarging structure 50 is formed by a plurality of protrusions 51, which project away from the outer tube-tube wall 31 a towards the inner tube 4 (not shown in FIG. 5). In the example of FIG. 5, the protrusions 51 are designed as webs 52, which extend along a common extension direction E. Here, the webs 52 are arranged spaced from one another transversely to the extension direction E subject to forming intermediate spaces 53. Practically, the protrusions 51 or the webs 52 can be arranged parallel to one another as shown in FIG. 5. Preferentially, the protrusions 51 or the webs 52 are integrally moulded on the outer tube-tube wall 31 a.

FIG. 6 exemplarily shows a version of the example of FIG. 5. In the example of FIG. 6, an aperture 57 each is formed in a plurality of webs 52 arranged transversely to the extension direction E. Said aperture 57 fluidically connects two intermediate spaces 53, which are separated transversely to the extension direction E by the relevant web 52. As is clearly shown by FIG. 6, a plurality of the webs 52 can be provided with such an aperture 57. Position and dimensioning can differ with different apertures 57. However, forming all existing apertures 57 identical in terms of position and dimensioning is also conceivable (not shown in FIG. 6).

FIG. 7 exemplarily shows a further development of the example of FIG. 5. Accordingly, a plurality of interruptions 54 can be preferably equidistantly provided in the webs 52. The interruptions 54 can be formed in the manner of recesses which are formed at an end section located opposite the outer tube inner wall 31 a of the web 52 concerned, in the same. The interruptions 54 in webs 52 that are adjacent transversely to the extension direction E are arranged aligned with one another transversely to the extension direction E, so that communication channels 55 are formed, which extend transversely to the extension direction E and fluidically interconnect adjacent intermediate spaces 53 formed between the webs 52. In the example of FIG. 7, the surface area-enlarging structure 50 thus forms a rib structure 56 with a plurality of ribs 70, which are formed by the webs 52 interrupted by the interruptions 54.

FIG. 8 shows a version of the example of FIG. 7. In the example of FIG. 8, the interruptions 54 are arranged transversely to the extension direction E of adjacent webs 52 staggered relative to one another along the extension direction E. In this way, communication channels 55 are formed which fluidically interconnect a plurality of adjacent intermediate spaces 53 formed between the webs 52. Because of the staggered arrangement of the interruptions 54 in adjacent webs 52 along the extension direction E, the communication channels 55 extend along a channel direction R, which with the extension direction E of the webs 52 form an acute angle α. In the examples of the FIGS. 5 to 8, the individual protrusions 51 or webs 52, in a top view perpendicularly onto the outer tube-tube wall 31 a, extend in each case linearly along the extension direction E.

Compared with this, the FIGS. 9 and 10 show two further versions of the examples of FIG. 5, in each case in a schematic highly simplified top view of the outer tube-tube wall 31 a, in which the webs 52 are designed not linearly but curved. In the top view according to FIG. 9, the individual webs each have a wave-like geometry or contour and are, analogously to the example of FIG. 5, arranged equidistantly spaced from one another subject to forming intermediate spaces 53 transversely to the extension direction E. A polygonal geometry in the top view is also conceivable.

In the example of FIG. 9, the individual webs 52 are formed interruption-free. By contrast, a plurality of the webs 52 has interruptions 54 in the example of FIG. 10, which can be realised analogously to the example of the FIGS. 7 and 8. In the example of FIG. 10, every second web 52 has such interruptions transversely to the extension direction E. The above explanations regarding the interruptions 54 according to the FIGS. 7 and 8 are also true, insofar as practical, also for the example of FIG. 10.

Attention is now directed at the further version according to FIG. 12. In the example of FIG. 12, a web group 59 is shown, which is formed by a plurality of webs 52. As is evident from the representation of FIG. 12, the webs 52 of the web group 59 radially extend away from a virtual centre point M defined on the outer tube-tube wall 31 a. In versions of the example, configurations of the web group 59 are also conceivable, in which the webs 52 are arranged in a geometry other than that shown in the FIG. 12.

In a further development of the example of FIG. 12 schematically shown in the FIG. 13 it is shown that on the outer tube-tube wall 31 a a plurality of web groups 59 can also be provided, while these web groups 59 are preferentially arranged grid-like, i.e. the web groups 59 form a grid with a plurality of grid columns 63 a and a plurality of grid lines 63 b. In the example of FIG. 13 a grid of web groups 59 with two grid columns 63 a and two grid lines 63 b is exemplarily shown. It is clear that, in versions, a different number of grid columns 63 a or grid lines 63 b can also be provided.

The FIGS. 14 to 16 show three further versions of the surface area-enlarging structure 50. In these examples, the surface area-enlarging structure 50 comprises a plurality of dimpled protrusions 60 and/or dimpled recesses 61, which are arranged grid-like on the inside 62 of the outer tube-tube wall 31 a.

In the example of the FIGS. 14 to 16, the inside 62 of the outer tube-tube wall 31 a facing the inner tube 2 is shown in each case. In the example of the FIG. 16, dimpled protrusions 60 are provided which project from the inside 62 of the outer tube-tube wall 31 a into the outer tube interior space 3, i.e. towards the inner tube 4. Compared with this, dimpled recesses 61 are provided in the example of FIG. 15, which project from the outer tube-tube wall 31 a to the outside, towards the thermoelectric modules 10.

In FIG. 14, a combination of the example of FIGS. 15 and 16 is shown. In this version, the grid-like arrangement comprises a plurality of grid columns 63 a, wherein adjacent grid columns 63 are alternately formed by protrusions 60 and recesses 61. The dimpled protrusions 60 respectively and/or recesses 61 according to the FIGS. 14 to 16 can have a circular geometry in the top view of the outer tube-tube wall. In versions, other suitable round or non-round geometries are also conceivable (not shown).

FIG. 17 shows a version of the example of FIG. 14 in a perspective representation. In the example of FIG. 17, the surface area-enlarging structure 50 comprises protrusions 60 arranged grid-like on the outer tube-tube wall 31 a. Analogous to FIG. 14, the grid-like arrangement comprises a plurality of grid columns 63 a and a plurality of grid lines 63 b. In the example of FIG. 17, the protrusions 60 each have a cylindrical geometry in the top view of the outer tube-tube wall 31 a. This is illustrated by the representation of FIG. 18, which exemplarily shows three protrusions 60 in a longitudinal section along the section line X-X of FIG. 17. In the example of the FIG. 18, the protrusions 60 each have the same height h, which is measured perpendicularly to the inside 62 away from the outer tube-tube wall 31 a. Compared with this, the FIG. 19 shows a version in which the heights of the protrusions 60 have different values h1, h2. A configuration in which the height of an individual projection varies is also conceivable.

In two further versions shown in the FIGS. 20 and 21, the protrusions 60 taper away from the outer tube-tube wall 31 a. In the example of the FIG. 20, the protrusions 60 each have the geometry of a truncated cone. In the example of the FIG. 21, the protrusions 60 are designed each terminating in a point. The version of FIG. 22 shows protrusions 60 the end section 65 of which facing away from the outer tube-tube wall 31 a is convex or, alternatively to this, has a concave geometry.

In FIG. 23 a version of the FIG. 5 is shown, but which can also be combined with the examples of the FIGS. 6 to 22. In the example of the FIG. 23, the outer tube-tube wall 31 a with the surface area-enlarging structure 50 is not designed flat as is shown in the example of the FIGS. 5 to 22. On the contrary, the outer tube-tube wall 31 a with the surface area-enlarging structure 50 comprises at least one first flat wall section 64 a. The first flat wall section 64 a merges at an angle into a second flat wall section 64 b. In the example of FIG. 23, the two wall sections 64 a, 64 b are arranged at an obtuse angle β to one another. In versions, other intermediate angles are also conceivable however.

In conclusion, attention is directed at the representation of FIG. 11. The FIG. 11 shows a version of the example of FIG. 14. In the example of the FIG. 11, the surface area-enlarging structure 50 comprises protrusions 60 which are arranged grid-like. Analogously to the version according to FIG. 14, the grid-like arrangement comprises a plurality of grid columns 63 a and a plurality of grid lines 63 b. In the example of the FIG. 11, the protrusions 60 each have the contour or geometry of a segment of a circle in the top view of the outer tube-tube wall 31 a. 

1. An exhaust gas heat exchanger for a motor vehicle comprising: an outer tube extending along a longitudinal direction configured to be flowed-through by a hot gas, the outer tube defining an outer tube interior space and in a cross section perpendicular to the longitudinal direction, comprises at least two outer tube-tube walls, an inner tube arranged in the outer tube interior space extending along the longitudinal direction, wherein a longitudinal end of the inner tube is closed and defines an inner tube interior space and in the cross section perpendicular to the longitudinal direction, comprises at least two inner tube-tube walls, wherein at least one of the at least two inner tube-tube walls includes a plurality of apertures, wherein the inner tube interior space fluidically communicates with the outer tube interior space via the plurality of apertures, wherein a plurality of thermoelectric modules are arranged on an outside of the at least two outer tube-tube walls and each include a hot side facing the outer tube and a cold side facing away from the outer tube, wherein at least one coolant tube configured to be flowed-through by a coolant is arranged on the cold side of at least one of the plurality of thermoelectric modules, wherein an inside of at least one of the at least two outer tube-tube walls includes at least one surface area-enlarging structure.
 2. The heat exchanger according to claim 1, wherein the at least one surface area-enlarging structure, with respect to the longitudinal direction, is disposed in a region of at least one of the plurality of thermoelectric modules.
 3. The heat exchanger according to claim 1, wherein the at least one surface area-enlarging structure is disposed opposite at least one aperture of the plurality of apertures, so that the hot gas exiting the at least one aperture at least partly strikes the at least one surface area-enlarging structure.
 4. The heat exchanger according to claim 1, wherein the at least one surface area-enlarging structure projects from at least one of the at least two outer tube-tube walls away towards the inner tube and is integrally moulded on the outer tube.
 5. The heat exchanger according to claim 1, wherein the at least one surface area-enlarging structure comprises a plurality of protrusions projecting away from the at least one outer tube-tube wall towards the inner tube.
 6. The heat exchanger according to claim 5, wherein the plurality of protrusions comprise a plurality of webs extending along an extension direction spaced from one another to define a plurality of intermediate spaces.
 7. The heat exchanger according to claim 5, wherein one of the plurality of protrusions or the plurality of webs, in a top view of the at least two outer tube-tube walls, extend along an extension direction at least one of linearly and non-linearly at least in sections.
 8. The heat exchanger according to claim 5, wherein one of the plurality of protrusions or the plurality of webs comprise a wave-like geometry in a top view.
 9. The heat exchanger according to claim 5, wherein a plurality of webs form a web group, and the plurality of webs of the web group radially extend away from a virtual centre point defined on at least one of the at least two outer tube-tube walls.
 10. The heat exchanger according to claim 9, wherein on at least one of the at least two outer tube-tube walls a plurality of web groups are arranged grid-like with at least two grid columns and with at least two grid lines.
 11. The heat exchanger according to claim 5, wherein at least one of the plurality of protrusions or the plurality of webs are arranged parallel to one another.
 12. The heat exchanger according to claim 6, wherein at least one of the plurality of protrusions or the plurality of webs along the extension direction each have a plurality of interruptions, the plurality of interruptions each fluidically interconnecting two adjacent intermediate spaces.
 13. The heat exchanger according to claim 12, wherein the plurality of interruptions of one of the adjacent plurality of protrusions or the plurality of webs along the extension direction are staggered relative to one another so that through the plurality of interruptions arranged staggered, a plurality of communication channels are defined and fluidically interconnect a plurality of adjacent intermediate spaces between one of the plurality of protrusions or the plurality of webs.
 14. The heat exchanger according to claim 13, wherein the plurality of communication channels extend along a channel direction, the channel direction forming an acute angle with the extension direction of one of the plurality of protrusions or the plurality of webs.
 15. The heat exchanger according to claim 5, wherein at least one web of the plurality of webs includes an aperture fluidically interconnecting two adjacent intermediate spaces of the plurality of intermediate spaces.
 16. The heat exchanger according to claim 1, wherein the at least one surface area-enlarging structure comprises at least one of a plurality of dimpled protrusions and a plurality of dimpled recesses arranged grid-like on an inside of at least one of the at least two outer tube-tube walls.
 17. The heat exchanger according to claim 16, wherein the grid-like arrangement comprises at least two grid columns, wherein adjacent grid columns are alternately formed by one of the plurality of protrusions or the plurality of recesses.
 18. The heat exchanger according to claim 16, wherein at least one of the plurality of protrusions and the plurality of recesses comprise a round, circular geometry in a top view of one of the at least two outer tube-tube walls.
 19. The heat exchanger according to claim 16, wherein at least one projection of the plurality of projections and at least one recess of the plurality of recesses tapers, conically, away from at least one of the at least two outer tube-tube walls.
 20. The heat exchanger according to claim 16, wherein one of: at least one of the at least two outer tube-tube walls with the at least one surface area-enlarging structure is; or at least one of the at least two outer tube-tube walls with the at least one surface area-enlarging structure comprises at least one first flat wall section that merges into a second flat wall section, arranged at an obtuse angle to the first wall section).
 21. A heat exchanger arrangement, comprising: at least two heat exchangers arranged on top of one another, and stacked onto one another, wherein the at least two heat exchangers fluidically communicate with one another via at least one common gas outlet configured to discharging a hot gas from the heat exchange arrangement.
 22. A motor vehicle comprising: an internal combustion engine including an exhaust system; a heat exchanger interacting with the exhaust system, the heat exchanger comprising one of: an outer tube extending along a longitudinal direction configured to be flowed-through by a hot gas, the outer tube defining an outer tube interior space and in a cross section perpendicular to the longitudinal direction, comprises at least two outer tube-tube walls, an inner tube arranged in the outer tube interior space extending along the longitudinal direction, wherein a longitudinal end of the inner tube is closed and defines an inner tube interior space and in the cross section perpendicular to the longitudinal direction, comprises at least two inner tube-tube walls, wherein at least one of the at least two inner tube-tube walls includes a plurality of apertures, wherein the inner tube interior space fluidically communicates with the outer tube interior space via the plurality of apertures, wherein a plurality of thermoelectric modules are arranged on an outside of the at least two outer tube-tube walls and each include a hot side facing the outer tube and a cold side facing away from the outer tube, wherein at least one coolant tube configured to be flowed-through by a coolant is arranged on the cold side of at least one of the plurality of thermoelectric modules, wherein an inside of at least one of the at least two outer tube-tube walls includes at least one surface area-enlarging structure; or at least two heat exchangers arranged on top of one another and stacked onto one another, wherein the at least two heat exchangers fluidically communicate with one another via at least one common gas outlet configured to discharging a hot gas from the heat exchange arrangement. 